The aim of the present invention is to provide a process for the conversion of at least one cut selected from the group formed by olefinic C.sub.4 cuts and olefinic C.sub.5 cuts to an ether (an alkyl-tertiobutylether or an alkyl-tertioamylether) and to propylene. When the cut originates from a steam cracking operation, a further aim of the present invention is to optimise the relative ethylene-propylene selectivity of the steam cracking procedure using this process.
Steam cracking of feeds constituted by light paraffin cuts supplies ethylene and propylene for the petrochemical industry. It also provides a number of other heavier products, in particular a C.sub.4 hydrocarbon cut which contains mainly 1,3-butadiene, isobutene, n-butenes and butanes, accompanied by traces of acetylenic hydrocarbons, and a C.sub.5 hydrocarbon cut which contains mainly C.sub.5 diolefins, methylbutenes, n-pentenes and pentanes, accompanied by traces of acetylenic hydrocarbons.
Likewise, the catalytic cracking of heavy hydrocarbon feeds, in particular fluid catalytic cracking (FCC), produces lighter products, among them a C.sub.4 hydrocarbon cut which contains mainly isobutane, isobutene, n-butenes and butanes, accompanied by small quantities of 1,3-butadiene and acetlyenic hydrocarbons, and a C.sub.5 hydrocarbon cut which contains mainly pentanes, methylbutenes and n-pentenes, accompanied by small quantities of C.sub.5 diolefins and acetlyenic hydrocarbons.
Until recently, only 1,3-butadiene and isobutene were of use in the polymer industry, in particular in the tire industry for the former. An increase in tire lifetime and a relative stagnation of demand has led to a surplus of butadiene which is not used to any great extent. In contrast, isobutene has gained in importance as it can be used to synthesize ethers which are used as additives for motor fuels.